NetQoS is offering a free tool, the NetQoS Latency Calculator to help network engineers ensure application performance across the WAN.
The company claims this tool allows you to model network latency under a number of different scenarios. It models a client-server environment, where both client and server are attached to local area networks, and each network is attached to a router. The clientside and server-side routers are attached through some kind of wide area link. To calculate latency times, the tool also lets you input arbitrary request and response sizes, and lets you set delays for the client itself, claims NetQoS.
NetQoS Latency Calculator Screenshot:
Then, to model the WAN portion of the connection, you can set router latency, wide area link speed and distance for each of a pair of routers. On the server side, you can set server latency and response size. You can then click the Calculate button to produce response latency and request latency values, with accompanying pie charts to show how overall delay breaks across the various input values provided. You can also use the input data to produce a WAN bar chart that helps model variable data rates for frame relay or constant bit rates on T1 links, claims NetQoS.
 "The latency calculator will tell you how long it would take to do an FTP transfer with different size files, for example,” said Bill Alderson - creator of the calculator and Technology Consulting Officer for NetQoS. "The calculator counts the number of round trips that are required and you can make the size whatever you’d like. Instead of having a packet size with a 1500 or an 8000 byte MTU maximum, you can simply crank in a 450GB file, and it’ll tell you how long it’ll take to serialize that file across the links you have selected." |
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Latency
Hello Sir,
How do i measure Latency and JItter for VoIP network.
Is there any Command line interface which will give me any way to calculate the Latency.
Thank You.
Bill Alderson Technology Consulting Officer for NetQoS Responds
Bill Alderson Technology Consulting Officer for NetQoS Responds:
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VoIP is two half duplex UDP communication streams, there are no response or acknowledgements of the data. That makes measuring latency difficult for stream protocol applications.
As each phone receives a UDP stream it maintains a latency buffer to eliminate minor variations in jitter. The receive chipset calculates its perceived jitter and reports it to the other phone and the call manager.
Network analyzers pickup and decode these statistics – but monitoring solutions such as NetQoS VoIP Monitor pick up and database these statistics and score them by direction, time, and location to find exceptions from the norm.
We all know when things are going well on the network as there are "no complaints" and when complaints start occurring it’s too late to engage an analyst in a manual manner as the problem is now gone – but the complaints of the behavior continue and are remembered by the users!
The Latency calculator can be used to determine theoretical network queuing, transmission distance and serialization delay caused by link speeds (typically the least common denominator link speed has the greatest affect). So if you are wanting to know the one way latency of a VoIP call from NYC to Qatar of 6700 miles, you’d put in the following data into the calculator:
The actual round trip ping is quite long at 240ms and perhaps is routed across much longer than 6700 miles. Round trip monitoring of other applications can be used to get an idea of what the one way latency is – but remember that you are not concerned with "normal or quiescent" but rather exceptions which cause issues.
BTW: Its not optimal to use VoIP for one way latencies beyond 150 – 200ms and conferencing is near impossible beyond such latency. So the best thing is to monitor and database your VoIP solution to catch exceptions!
View more information about NetQoS VoIP Monitor.
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Sincerely,
Brad Reese
http://www.BradReese.Com
NetQoS Latency Calculator (underlying formula)
Is it possible to see the underlying latency formula used in your calculator. If proprietary, maybe you can share what factor is applied to the speed of light.
Thanks,
Latency Calculator Calculation
Craig, the calculation is pretty basic.
LAN Calculation:
Packetsize / (linkspeed-in-bits-per-second/8)
WAN Insertion Delay
Packetsize / (linkspeed-in-bits-per-second/8)
The WAN distance latency is roughly 1ms per 100 miles on a point-to-point link and 1.5ms per 100 miles on links such as Frame Relay.
If you add the LAN insertion delays, WAN insertion delays, and the amount of time spent waiting on the WAN link, you get the overall latency.
You do need to know the number of "application turns" to accurately calculate the overall delay. This is the number of requests make by the client that require the application to wait the full roundtrip delay of the circuit. For example when copying a file using Server Message Block (SMB), aka CIFS, each SMB Read Request counts as a turn. If the roundtrip delay of the circuit is 100ms, you will need to add 100ms for each read request.